Has anyone had an issue of zero offset fluctuation after a battery change? I recently changed the batteries in mine and now the zero offset seems to be all over the map. When indoors it's anywhere between 800 and 1100. However when going outside i've had it go anywhere from 55 to 2400 and the power numbers are either unrealistically low or high. Indoors the number is stable, it just changes from day to day.

haha i suppose so. It wasn't done by SRM however i did have someone qualified put it in. Needless to say when indoors it's stable, though a little on the high side. Pre Battery change zero offset was in the 600 range. It's just when out in the cold that it goes all wonky. I know temperature can affect strain gauges but this much?

by stable i mean the zero offset doesn't drift. It just changes. (which i know is a drift but it stays at a certain number for an extended period)

Last edited by pcates on Thu Apr 11, 2013 6:24 pm, edited 2 times in total.

Calibration was done 3x afterwards. All were in the same range as the original slope. Chainring bolts were torqued to suggested 10nm. Now I did crank the crank bolt pretty tight since its an FSA and my torque wrench doesn't go that high. I wonder if that may be the reason for the higher then normal zero offset (when in the house at a steady temp it's in the 800 range up from the low 600 range before the battery change). As I mentioned the zero offset is stable. Just high. When I went to check the zero offset after doing a couple hill repeats it was around 1400 so I'm not sure if this is due to some sort of residual strain in the gauges. But the power numbers were accurate based on previous outputs.

Where I was having the big issue was with temperature. It seemed when the temp was hovering around 0 (32 for you guys to the south i was getting all sorts of wonky numbers. 55 for a zero offset and 65watts going uphill.

Since the numbers, now that its above freezing, seem to be ok now this may all be a moot issue. Still I'm curious to know the reason behind all this in case it becomes an issue again in the future.

Sounds like the replacement battery may be even more depleted than the original. Have you tried swapping them? I test batteries before installing them. Non-rechargeable lithium batteries (including popular button cells like CR2032s) cannot be tested by measuring open circuit voltage. They need to be tested under load. Many will read 3-3.2V but dive to 0.8-1.2V under load.

What I do is put a 100 Ohm resistor across the terminals and measure the voltage in parallel.

^^ that's a very good point. The replacements I found were 3.5V as opposed to 3.6V. I didn't think that would make much of a difference but if they're running low then perhaps that's the issue. Thanks for the link btw.

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